Who should be the owner of newly created files when the creator is in the local Administrators group

simo idra at samba.org
Sun Apr 29 11:39:05 MDT 2012

On Sat, 2012-04-28 at 21:52 -0700, Richard Sharpe wrote: 
> Hi folks,
> Here http://technet.microsoft.com/en-us/library/cc781716%28v=WS.10%29.aspx
> it says:
> "Note
>     When users who are members of the local Administrators group
> access objects on Windows Server 2003, the Default Owner field in the
> user’s access token contains the SID for the Administrators group, not
> the SID for the user. A similar rule applies to users who access
> objects in Active Directory. If the user is a member of the Domain
> Admins group, the Default Owner field in the user’s access token
> contains the SID for the Domain Admins group. In both cases, objects
> that the user creates or takes ownership of are owned by the group,
> not by the individual user."
> This suggests that we currently do the wrong thing, I think, when we
> create a file and the creator is in the local Administrators group.

The problem is that in Posix, groups cannot own files.

Around the first time I put my hands in Idmap (2002/3 ?) I had a
discussion with Tridge and Jeremy about changing samba to always
allocate both a uid and a gid for any SID for 2 simple reasons:
1) It allows us to avoid resolving the SID at allocation time if we do
not want to as we do not need anymore to check what it is.
2) It would allow groups to own files by using the "Group's UID".
At that time it wasn't accepted as an idea, so samba 3.x never gained
this ability.

Fast forward to samba 4 and now there is IDMAP_BOTH, which is
essentially that proposal come true :-)

Unfortunately we still do not support IDMAP_BOTH in samba 3.
Point is that it is an incompatible change, that you cannot turn on
implicitly in existing installations.

That said I do support this method, so much so that in FreeIPA I also by
default merged the id space, long ago, and effectively only have a
unified ID space in the default install, as it makes it easier to handle
personal user groups w/o polluting the tree with real fully featured

So long story short, yes we should do what is suggested there, but
before we can do it, we need to add the option to use IDMAP_BOTH in the
File server, optionally. The ACL code needs to be changed to understand
IDMAP_BOTH and Winbindd also need to be changed so that a direct lookup
of a UID beloging to a Group returns an actual disabled user with the
same name of the group, the same ID, but no password, no home, no shell,
and an indicator in the Gecos that this is actually a group. We should
never returns these entries in enumerations though. As they are not real
users and you do not want to pollute user's lists in those installations
that want to be able to list users and groups.


Simo Sorce
Samba Team GPL Compliance Officer <simo at samba.org>
Principal Software Engineer at Red Hat, Inc. <simo at redhat.com>

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